The present invention relates to control of a suspension system of an automobile and more particularly to an active suspension control method for controlling an active suspension system by injection or discharge of a fluid into or from suspension cylinders.
Conventionally, suspension cylinders are controlled by feedback of control based on lateral acceleration or vertical acceleration of a sprung mass supported above each suspension cylinder or by feed forward control based on steering angle or vehicle speed. These types of techniques and related techniques are disclosed, for example, in Japanese Patent Un-examined Publications JP-A-63-242707 and JP-A-63-269709.
The conventional active suspension control methods for suspension cylinder control have the following problems:
(i) They do not allow for the transient roll and pitch characteristics of a vehicle body during vehicle traveling, and so a control command from a controller cannot clearly follow changes in the roll and pitch angles.
(ii) They do not allow for changes in the attitude of the vehicle body caused by different kinds braking, such as engine braking, foot braking or hand braking, and so changes in the pitch angle cannot be sufficiently suppressed.
(iii) They do not allow for the information from an acceleration sensor when the vehicle body is tilted, and so cannot sufficiently suppress changes in the attitude of the vehicle body when the same is tilted, for example, on a slope.
(iv) They do not allow for manual control of active suspensions and cannot adjust the lengths of the suspension cylinders when the vehicle is at a stop.
(v) They do not allow for changes in the energy required for operation of the suspension cylinders, and the discharge and so injection of fluid from and into the suspension cylinders do not closely follow rapid changes in the attitude of the vehicle body.
(vi) They do not allow for the inability to control the suspension cylinders caused by the failure of means for feeding fluid to the suspension cylinders or breakage of a main fluid tank.